As the power to be dissipated by semiconductor devices increases with time, a problem arises: over time the thermal conductivity of the available materials becomes too low to conduct the heat from the semiconductor device to the fins with an acceptably low temperature drop. The thermal power density emerging from the semiconductor devices will be so high that even copper or silver spreader plates will not be adequate. Compounding this problem is that circuit boards are typically housed in enclosures that are increasingly becoming smaller in size.
For relatively low-power systems, air cooling and heat sink techniques often adequately maintain lower operating temperatures to such electronic components. Application of printed circuit boards that employ high power electronic components demanded by such equipment used, often require liquid cooling to minimize the cooling system size, and heat transfer medium required transmitting larger amount of heat rate using relatively smaller size cooling system. Several different liquid-cooling methods have been proposed in the field of cooling high power dissipating electronic components mounted on printed circuit boards. A typical processor board can contain a multiplicity of CPU modules with associated cache memory, ASICs, and DC—DC converters. The total power dissipation from a similarly configured board can reach more than 600 W. Similar components can exist on each side of a board. With microprocessor power dissipation continuing to increase while the space available for a thermal solution decreases, it becomes necessary to improve heat dissipation by the CPU and associated components. One such improvement is a single-phase forced-liquid cooling system.
The primary components of a single-phase forced-liquid cooling system are a pump, a heat exchanger, a liquid-cooled cold plate and some associated tubing required to interconnect the components and put them in fluid communication (i.e., provide passageways and/or orifices for fluid to travel between the components). Heat is dissipated by the microprocessor, and/or other power consuming component, and transferred to the liquid circulating through the cold plate, with which the component is in intimate contact. The liquid increases in temperature without changing its phase as it absorbs heat. The liquid is then moved to a heat exchanger, via the pump, where the heat is transferred to ambient air, resulting in a reduction in temperature of the liquid. The cycle is repeated when the liquid re-enters the cold plate. One of the more popular liquid-cooling mechanisms employs an aluminum cover assembly that mounts to a circuit board in overlaying close-fitting relationship to the surface-mounted electronics. This kind of cooling apparatus is commonly referred to as a cold plate.
Conventional cold plates typically comprise a relatively flat thermally conductive body formed with an engagement surface that closely mirrors the surface configuration or topology of the circuit board. An internal cooling channel is formed in the plate to circulate cooling fluid through the body and draw heat away from the cold plate during operation. The plate mounts to the circuit board using separate mechanical hardware, e.g., spring loaded clips and the like, with the respective electronic components often nested in corresponding close-fitting recesses. While conventional cold plates offer significant cooling advantages for printed circuit boards, as compared to air-cooled systems, some of the drawbacks involve cost and reliability. Typically, the costs associated with cold plates often reflect long lead times and complex manufacturing operations, which most often may lead to lower reliability. Consequently the expense to employ a traditional cold plate system and its associated mounting hardware, coupled with reliability issues in a printed circuit board environment, is often undesirably high cost and lower reliability.
In an effort to address these problems, those skilled in the art have advanced many proposals for design and manufacturing cold plates. For example, in U.S. Pat. No. 6,305,463, issued to Salmonson, discloses a cold plate that provides air or liquid cooling for a computer circuit module and has at least one mounting plate with a board mounting surface on one side for carrying a printed circuit board assembly and a cooling surface located on the other side. A cover is disposed parallel to and spaced apart from the mounting plate with a cooling chamber defined between the two. U.S. Pat. No. 6,587,343 issued to Novotny, et al., discloses a water-cooled system and method for cooling electronic components. The system includes a surface with at least one electronic component coupled to the surface, where the at least one electronic component includes an integrated circuit. A closed-loop fluidic circuit is coupled to the surface for removing heat from the integrated circuit. The closed-loop fluidic circuit includes a heat exchanger. U.S. Pat. No. 5,050,037, issued to Yamamoto, et al., discloses a printed circuit board assembly having a printed circuit board mounted, on both faces with heat generative electronic circuit components, such as integrated circuit chips, and a pair of liquid-cooling modules arranged on both sides of the printed circuit board. Each of the liquid-cooling modules is provided with a liquid cooling plate having liquid coolant supply heads and a plurality of resilient heat transfer units held by the liquid-cooling plate and arranged in compressive contact with the electronic circuit components on both faces of the printed circuit board.
What is needed and has been heretofore unavailable is a high-performance, cost-effective cold plate configuration that lends itself to a high level of manufacturability, and a method that implements straightforward design and fabrication steps to minimize costs and production delays, which in turn simplifies the design of the cooling system, and its components. The cold plate of the present invention satisfies these needs.